Fetal alcohol exposure results in persistent cognitive dysfunctions that may be secondary to damage of the hippocampus, a brain region involved in learning and memory. During development, the hippocampus displays a pattern of network-driven neuronal activity known as giant depolarizing potentials (GDPs). These events are mediated, in part, by GABAA receptors, which are depolarizing in immature neurons that express low levels of the Cl exporter, KCC2, and thus, have higher [Cl]i. Preliminary data indicates that ethanol (EtOH) potently increases the frequency of GDPs and that the underlying mechanism of this effect is an increase in the probability of GABA and glutamate release at interneurons. We hypothesize that EtOH increases transmitter release at mossy fibers, which can co-release GABA and glutamate in the developing hippocampus. Alternatively, GABA could be released from interneurons terminals and glutamate from pyramidal neuronal terminals. Moreover, we hypothesize that the EtOH-induced increase of GDP frequency will result in an elevation of [CA2+]i, which will lead to downregulation of KCC2 via an increase in BDNF levels, resulting in a delayed switch in the actions of GABAA receptors from excitatory to inhibitory. Specific Aim #1 is to determine the source of the EtOH-induced increase in GABA and glutamate. Using patch-clamp electrophyisiological techniques and neonatal hippocampal slices, we will measure paired-pulse plasticity of GABAA and AMPA receptor-mediated postsynaptic currents evoked in CA3 interneurons by stimulation of mossy fibers, internuerons, or pyramidal cells. Specific Aim #2 is to determine if the EtOH-induced increase of GDP frequency elevates [CA2+]i. We propose to use CA2+ imaging and patch-clamp techniques to address this possibilty and will also investigate the effect of EtOH on the degree of synchronization of developing neuronal ensembles. Specific Aim #3 is to assess whether EtOH modulation of GDPs affects KCC2 levels in vitro. We will also investigate the effect of EtOH on BDNF and pCREB levels. Specific Aim #4 is to determine the impact of long-term EtOH exposure in vivo on GDP-driven network activity and KCC2 levels. We will expose neonatal rats along their dams to EtOH via inhalation chambers and measure expression of KCC2 levels and the switch in the actions of GABAA receptors from excitatory to inhibitory. We will also investigate whether in vivo EtOH exposure induces alterations in synchronized neuronal activity. Collectively, these studies will establish that network neuronal activity driven by the excitatory actions of GABAA is a novel and important target of the actions of EtOH during hippocampal development.